1. Field of the Invention
The present invention relates to a radiation noise suppressing component attachment structure for suppressing noises radiated from an electronic component, a circuit board, or other similar noise emitting apparatus.
2. Description of the Related Art
Generally, a conventional electromagnetic wave absorber for absorbing unnecessary electromagnetic wave noises is defined by a magnetic sheet formed by mixing ferrite or magnetic metal powder with a resin, and processing the mixed material to form a sheet. In addition, another conventional noise suppressing component contains a conductor layer provided on the surface or inside of the magnetic sheet, in which the conductor layer is used as a reflection layer for electromagnetic waves. In this magnetic sheet having the conductor layer, radiation noises are absorbed by the above-described magnetic sheet, and moreover, the radiation noises, which are attenuated in the magnetic sheet, are reflected from the conductor layer, and passed through the magnetic sheet again, where the radiation noises are further attenuated.
However, for practical use, these electromagnetic wave absorbers each are simply bonded to the upper sides of radiation noise generating sources such as electronic components, wiring on circuit boards, and other elements which generate radiation noises. Such an attachment structure has the problem that the radiation noise inhibiting effect achieves a noise prevention amount of only several dB and therefore, a much greater radiation noise inhibiting effect is not possible.
To overcome the problems described above, preferred embodiments of the present invention provide a radiation noise inhibiting component attachment structure which is simple but achieves a very large radiation noise inhibiting effect.
According to a preferred embodiment of the present invention, a radiation noise inhibiting component attachment structure includes a radiation noise inhibiting component including a magnetic sheet and a conductor layer on the magnetic sheet, the magnetic sheet being arranged to substantially cover a radiation noise generating source and so as to face the radiation noise generating source, and the conductor layer is arranged to substantially cover the magnetic sheet and is grounded.
Preferably, the magnetic sheet is made of a magnetic powder mixed with at least one of a resin and a rubber, and the magnetic powder is made of at least one of ferrite and a magnetic metal. The conductor layer is preferably made of at least one member of the group consisting of metal foils, plating films, metal meshes, conductive pastes, conductive fibers, and conductive sheets.
With the unique structure and arrangement of elements described above, radiation noises radiated from the radiation noise generating source, are absorbed by the magnetic sheet so that the noises are attenuated, and then, are incident upon the conductor layer. Since the conductor layer is grounded, a part of the incident radiation noises are transmitted to the ground through the conductor layer. The remaining radiation noises are reflected from the conductor layer, and passed through the magnetic sheet again where the radiation noises are absorbed so as to be even further attenuated. Accordingly, the radiation noises radiated from the radiation noise generating source are considerably attenuated such that a much greater attenuation of noises is achieved as compared to conventional devices.
Further, in the radiation noise inhibiting component attachment structure according to preferred embodiments of the present invention, preferably, the conductor layer is substantially covered with another magnetic sheet. Accordingly, the radiation noise inhibiting component preferably has a sandwich structure in which the conductor layer is disposed between the two magnetic sheets. Leaking radiation noises, that is, the radiation noises which turn from the sides of the conductor layer toward the back side thereof without flowing through the conductor layer to the ground and also without being reflected from the conductor layer, are attenuated by the magnetic sheet which is disposed at the back of the conductor layer.
In addition, the thickness of the magnetic sheet provided between the radiation noise generating source and the conductor layer is preferably about 0.3 mm or more, so that the radiation noises can be attenuated by about 10 dB or more.
For the purpose of illustrating the present invention, there is shown in the drawings several forms and embodiments which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentality""s shown.